Micro carbon materials such as carbon black, ketjen black, fullerene, graphene and carbon nanotubes have been widely used in fields such as electronics and energy fields due to their electrical properties and thermal conductivity. Particularly, carbon nanotubes, one type of micro carbon fibers, are tube-type carbon having a thickness of 1 μm diameter or less, and are expected to be used and commercialized in various fields due to their high conductivity, tensile strength and thermal resistance caused from their unique structures.
However, despite such usefulness of carbon nanotubes, carbon nanotubes have limits in the use due to low solubility and dispersibility. In other words, carbon nanotubes have a problem in that they do not form a stably dispersed state and cause aggregation in an aqueous solution due to strong Van der Waals interaction between them.
In view of such a problem, various attempts have been made. Specifically, methods of dispersing carbon nanotubes into a dispersion medium through mechanical dispersion treatment such as ultrasonic treatment have been proposed. However, these methods have a problem in that, although dispersibility is excellent while irradiating ultrasonic waves, carbon nanotubes start to aggregate when ultrasonic irradiation is finished and aggregate when the carbon nanotube concentration increases.
In addition, methods of dispersing and stabilizing carbon nanotubes using various dispersants have been proposed. For example, methods of dispersing carbon nanotubes through ultrasonic treatment in water or N-methyl-2-pyrrolidone (hereinafter, NMP) using an anionic surfactant such as sodium dodecyl sulfonate or sodium dodecyl benzenesulfonate, or a nonionic surfactant such as Triton (registered trademark)-X-100 have been proposed. In addition, methods of dispersing carbon nanotubes into a dispersion medium such as water or NMP using a polymer-based dispersant such as polyvinyl pyrrolidone (hereinafter, EVP) or a cellulose derivative, a water-soluble polymer, instead of a surfactant have been proposed. However, these methods also have a problem in that handling becomes difficult when micro carbon fibers are dispersed into a dispersion medium in a high concentration due to an increase in the viscosity.
Accordingly, in order to expand carbon nanotube applications, preparing a dispersion liquid in which carbon nanotubes are uniformly dispersed into a dispersion medium is important.